INTRODUCTION 

Figure 1 shows a typical dc-to-dc converter configuration. As in many PWM controllers, the non-inverting input of the voltage feedback error amplifier is internally connected to the reference voltage, Vr. The output voltage of the converter is set by a resistor divider network R1 and R2. This configuration enables a fixed output voltage that is equal to or greater than the reference voltage. But in many power conversion designs, it is useful to vary the output to a value lower than the reference voltage and to dynamically adjust the output voltage.